Motor drive device capable of informing malfunction in operation of fan, and method thereof

ABSTRACT

A motor drive device can improve the accuracy of detection of malfunction in a fan. The motor drive device includes a fan, a fan controller for controlling the fan, a rotation speed detecting part for detecting the rotation speed of the fan, a relationship acquiring part for acquiring a relationship between a time elapsed from a time point, at which the fan controller changes the rotation speed, and the rotation speed detected by the rotation speed detecting part, a malfunction determining part for determining whether the relationship acquired by the relationship acquiring part is different from a predetermined standard, and a malfunction signal generating part for generating a signal representing the occurrence of malfunction in the fan, when it is determined that the relationship is different from the standard.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a motor drive device capable of informing auser of a malfunction in the operation of a fan, and a method thereof.

2. Description of the Related Art

A device capable of detecting a malfunction in the rotation speed of afan has been known (see, for example, Japanese Unexamined PatentPublication (Kokai) No. 10-28394).

In a motor drive device for driving a servomotor embedded in a machinetool or an industrial robot, a control scheme for stopping the operationof the motor drive device when a malfunction in a fan is detected isused in some cases.

In this instance, detection of malfunction in the fan directly resultsin stopping of the operation process. Thus, in the field of motordriving motors, in terms of improving working efficiency, earlydetection of a warning sign of malfunction in a fan has been required.

SUMMARY OF THE INVENTION

In an aspect of the invention, a motor drive device includes a fan, afan controller which controls the fan, a rotation speed detecting partwhich detects the rotation speed of the fan, and a relationshipacquiring part which acquires a relationship between a time elapsed froma time point, at which the fan controller changes the rotation speed,and the rotation speed detected by the rotation speed detecting part.

The motor drive device includes a malfunction determining part whichdetermines whether the relationship acquired by the relationshipacquiring part is different from a predetermined standard, and amalfunction signal generating part which generates a signal indicatingthat a malfunction occurs in the fan when the malfunction determiningpart determines that the relationship is different from the standard.

The relationship acquiring part may acquire, as the relationship, anamount of change in the rotation speed detected by the rotation speeddetecting part within a time period until a predetermined time elapsesfrom the time point at which the fan controller sends to the fan acommand for changing the rotation speed. The malfunction determiningpart may determine that the relationship is different from the standardwhen the acquired amount of change is greater or smaller than apredetermined threshold value.

The relationship acquiring part may calculate, as the relationship, aratio of an amount of change in the rotation speed detected by therotation speed detecting part within a time period until a predeterminedtime elapses from the time point at which the fan controller sends tothe fan a command for changing the rotation speed, to the standard. Themalfunction determining part may determine that the relationship isdifferent from the standard when the ratio is greater or smaller than apredetermined threshold value.

The relationship acquiring part may acquire, as the relationship, a timeuntil the rotation speed detected by the rotation speed detecting partchanges from a first rotation speed to a second rotation speed differentfrom the first rotation speed when the fan controller sends to the fan acommand for changing the rotation speed from the first rotation speed tothe second rotation speed.

The malfunction determining part may determine that the relationship isdifferent from the standard when the acquired time is greater or smallerthan a predetermined threshold value. The motor drive device may furtherinclude a timer which measures a time from a time point at which the fancontroller changes the rotation speed.

The motor drive device may further include a storage which stores therotation speed detected by the rotation speed detecting part or the timefrom the time point at which the fan controller changes the rotationspeed. The motor drive device may further include an alarm output partwhich receives the signal and outputs an alarm to a user.

In another aspect of the invention, a method of notifying a user of anoccurrence of a malfunction in a fan provided at a motor drive devicecomprises changing a rotation speed of the fan, and detecting therotation speed when changing the rotation speed.

The method comprises acquiring a relationship between a time elapsedfrom a time point, at which the rotation speed is changed, and thedetected rotation speed, determining whether the acquired relationshipis different from a predetermined standard, and notifying to a user thata malfunction occurs in the fan when determining that the relationshipis different from the standard.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned or other objects, features, and advantages of theinvention will be clarified by the detailed description of embodimentswith reference to accompanying drawings, in which:

FIG. 1 is a perspective view of a motor drive device according to anembodiment of the invention;

FIG. 2 is a block diagram of the motor drive device shown in FIG. 1;

FIG. 3 is a front view of the fan shown in FIG. 2;

FIG. 4 is a graph representing a relationship between the rotation speedof the fan and time when the rotation speed is decreased;

FIG. 5 is a graph representing a relationship between the rotation speedof the fan and time when the rotation speed is increased;

FIG. 6 is a flowchart of an example of the operation flow of the motordrive device shown in FIG. 1; and

FIG. 7 is a flowchart of another example of the operation flow of themotor drive device shown in FIG. 1.

DETAILED DESCRIPTION

Embodiments of the invention will be described below in detail withreference to the drawings. First, with reference to FIGS. 1 to 3, amotor drive device 10 according to an embodiment of the invention willbe described. The motor drive device 10 supplies electric power to aservomotor (not shown) built in e.g. a machine tool or industrial robotin order to drive the servomotor.

As shown in FIG. 1, the motor drive device 10 includes a housing 12. Thehousing 12 is e.g. a box-shaped member made of resin, and houses thereincomponents including a controller 16 described later. A through-hole 14is formed at the housing 12.

As shown in FIG. 2, the motor drive device 10 further includes thecontroller 16, a fan 18, a rotation speed detecting part 19, an alarmoutput part 20, a timer 22, and a storage 24. The controller 16 includese.g. a CPU, and is housed in the housing 12. The controller 16 directlyor indirectly controls each component of the motor drive device 10.

The fan 18 is housed in the housing 12 so as to face the through-hole 14formed at the housing 12. As shown in FIG. 3, the fan 18 includes arotator 28 having a plurality of vanes 26, and a fan motor 30 whichrotates the rotator 28.

The rotator 28 is arranged to be adjacent to the through-hole 14 formedat the housing 12. The fan motor 30 is connected to an inverter 32 (FIG.2). The inverter 32 supplies electric power to the fan motor 30 inaccordance with a command from the controller 16.

The fan motor 30 drives the rotator 28 to rotate at the rotation speedcorresponding to the electric power supplied from the inverter 32. Whenthe rotator 28 is rotated, an air in the housing 12 is discharged to theoutside through the through-hole 14, thereby the motor drive device 10is cooled.

The rotation speed detecting part 19 includes e.g. an encoder or Hallelement, and is attached to the fan 18. The rotation speed detectingpart 19 detects the rotation speed of the rotator 28 of the fan 18 inaccordance with a command from the controller 16, and sends data of thedetected rotation speed of the fan 18 to the controller 16.

The alarm output part 20 includes e.g. a speaker or display part, andoutputs a sound or image in accordance with a command from thecontroller 16. The timer 22 times an elapsed time from a given timepoint in accordance with a command from the controller 16.

The storage 24 includes e.g. a non-volatile memory such as an EEPROM(registered trademark) which can electrically delete and record data, ora random access memory such as DRAM or SRAM which can rapidly read outand write on data. The controller 16 can record data on, and delete datafrom the storage 24.

As the fan 18 is driven, foreign substances, such as dust or cuttingfluid, etc., gradually accumulate on the rotator 28 of the fan 18,thereby the rotation of the rotator 28 can be disturbed. The motor drivedevice 10 according to this embodiment detects such malfunction in thefan 18.

Below, with reference to FIGS. 4 and 5, the concept for detecting amalfunction of the fan 18 in the motor drive device 10 will bedescribed. FIG. 4 is a graph showing the relationship between rotationspeed R of the fan 18 and time t when the controller 16 sends a rotationspeed changing command to the fan motor 30 at a time point t₁ so as toreduces the rotation speed of the fan 18 from a rotation speed R₂ to arotation speed R₁.

On the other hand, FIG. 5 is a graph showing the relationship betweenrotation speed R of the fan 18 and time t when the controller 16 sends arotation speed changing command to the fan motor 30 at a time point t₄so as to increase the rotation speed of the fan 18 from a rotation speedR₄ to a rotation speed R₅.

A solid line 34 in FIG. 4 and a solid line 38 in

FIG. 5 represent characteristics when the fan 18 normally operates(hereinafter, referred as a “normal product”). On the other hand, abroken line 36 in FIG. 4 and a broken line 40 in FIG. 5 representcharacteristics when foreign substances attach to the rotator 28 of thefan 18, thereby an operational malfunction occurs in the fan 18(hereinafter, referred as a “malfunction product”).

As can been seen from FIG. 4, according to the normal product, when therotation speed R is decreased, the rotation speed R reduces relativelymoderately from the time point t₁, and reaches the rotation speed R₁ ata time point t₃. On the other hand, according to the malfunctionproduct, the rotation speed R decreases from the time point t₁ moresharply than in the normal product, and reaches the rotation speed R₁ ata time point t₂ (<t₃).

Thus, a remarkable difference is made between the relationship betweentime t and rotation speed R (hereinafter, the “t−R relationship”) of thenormal product after the time point t₁, and the t−R relationship afterthe time point t₁ of the malfunction product. This is caused by the factthat the rotation of the rotator 28 in the malfunction product isdisturbed by the foreign substances attached thereto.

The motor drive device 10 according to this embodiment detects amalfunction in the fan 18 by making use of the above-mentioneddifference between the t−R relationships of the normal product and themalfunction product. The t−R relationship in the fan 18 can be evaluatedby various parameters described below.

As an example, in FIG. 4, an amount of change δR_(ref) in the rotationspeed R of the normal product within a time period t¹⁻²(=t₂−t₁) isδR_(ref) ≈R₂−R₃. On the other hand, an amount of change δR in therotation speed R of the malfunction product within the time period t¹⁻²is δR≈R₂−R₁. As can been seen from FIG. 4, the amount of change δR inthe malfunction product is remarkably larger than the amount of changeδR_(ref) in the normal product.

Thus, a malfunction in the operating fan 18 can be detected by acquiringthe amount of change δR as a parameter representing the t−R relationshipof the fan 18, and comparing it with the δR_(ref) in the normal product,which is to be used as a standard.

As another example, a malfunction in the operating fan 18 can bedetected by calculating, as a parameter representing the t−Rrelationship in the fan 18, a ratio R of the amount of change δR to thestandard δR_(ref), i.e., R=δR/δR_(ref)≈(R₂−R₁)/(R₂−R₃) , and comparingthe ratio R with a predetermined threshold value.

As still another example, a time period t¹⁻³(=t₃−t₁) is necessary in thenormal product until the rotation speed R changes from R₂ to R₁, whereasa time period t¹⁻²(=t₂−t₁) is necessary in the malfunction product untilthe rotation speed R changes from R₂ to R₁. As seen from FIG. 4, thetime period t¹⁻² in the malfunction product is remarkably smaller thanthe time period t¹⁻³ in the normal product.

Accordingly, a malfunction in the operating fan 18 can be detected byobtaining the time period t¹⁻² as a parameter representing the t−Rrelationship in the fan 18, and comparing it with the time period t¹⁻³in the normal product, which is to be used as a standard.

As still another example, a malfunction in the operating fan 18 can bedetected by acquiring, as a parameter representing the t−R relationshipin the fan 18, a gradient δR/δt of the rotation speed R (i.e.,acceleration) in the time period t¹⁻², i.e., δR/δt=(R₂−R₁)/t¹⁻², andcomparing it with a gradient in the normal product, i.e.,δR_(ref)/δt=(R₂−R₃)/t¹⁻², which is to be used as a standard.

Referring to FIG. 5, according to the normal product, when the rotationspeed R increases, the rotation speed R increases relatively sharplyfrom the time point t₄, and reaches the rotation speed R₅ at a timepoint t₅. On the other hand, according to the malfunction product, therotation speed R increases from the time point t₄ more moderately thanin the characteristic of the normal product, and reaches the rotationspeed R₅ at a time point t₆.

Thus, when the rotation speed R increases, a remarkable difference ismade between the t−R relationship in the normal product and the t−Rrelationship in the malfunction product, after the time point t₄.Accordingly, a malfunction in the fan 18 to be inspected can be detectedby making use of such a difference in the t−R relationship between thenormal product and the malfunction product.

As an example, in FIG. 5, the amount of change δR_(ref) in the rotationspeed R of the normal product within the time period t⁴⁻⁵ from the timepoint t₄ to the time point t₅ (i.e., t⁴⁻⁵=t₅−t₄) is δR_(ref)=R₅−R₄. Onthe other hand, the amount of change δR in the rotation speed R of themalfunction product within the time period t⁴⁻⁵ is δR=R₆−R₄. As seenfrom FIG. 5, the amount of change δR of the malfunction product isremarkably smaller than the amount of change δR_(ref) of the normalproduct.

Accordingly, a malfunction in the operating fan 18 can be detected byacquiring the amount of change δR as a parameter representing the t−Rrelationship of the operating fan 18, and comparing it with the δR_(ref)of the normal product, which is to be used as a standard.

In another example, a malfunction of the operating fan 18 can bedetected by calculating, as a parameter representing the t−Rrelationship of the operating fan 18, a ratio R of the amount of changeδR to the standard δR_(ref), i.e., R=δR/δR_(ref)=(R₆−R₄)/(R₅−R₄), andcomparing the ratio R with a predetermined threshold value.

In still another example, referring to FIG. 5, a time periodt⁴⁻⁵(=t₅−t₄) is necessary in the normal product until the rotation speedR changes from R₄ to R₅, whereas a time period t⁴⁻⁶(=t₆−t₄) is necessaryin the malfunction product until the rotation speed R changes from R₄ toR₅. As can been seen from FIG. 5, the time period t⁴⁻⁶ of themalfunction product is remarkably greater than the time period t⁴⁻⁵ ofthe normal product.

Thus, a malfunction in the operating fan 18 can be detected by acquiringthe time period t⁴⁻⁶ as a parameter representing the t−R relationship ofthe operating fan 18, and comparing it with the time period t⁴⁻⁵ of thenormal product, which is to be used as a standard.

In still another example, a malfunction in the operating fan 18 can bedetected by acquiring the gradient δR/δt of the rotation speed R withinthe time period t⁴⁻⁵, i.e., δR/δt=(R₆−R₄)/t⁴⁻⁵, as a parameterrepresenting the t−R relationship of the operating fan 18, and comparingit with the gradient δR_(ref)/δt of the normal product, i.e.,δR_(ref)/δt=(R₅−R₄)/t⁴⁻⁵, which is to be used as a standard.

Thus, the motor drive device 10 according to this embodiment detectswhether a malfunction occurs in the fan 18, by making use of the variousparameters (δR, t¹⁻², δR/δt, t⁴⁻⁶) and standards (δR_(ref), t¹⁻³,δR_(ref)/δt, t⁴⁻⁵).

Next, with reference to FIG. 6, an example of the operation flow of themotor drive device 10 will be described. The flow shown in FIG. 6 isstarted when the controller 16 receives from a user, host controller orcontrol program a malfunction inspection command for inspecting anoperational malfunction in the fan 18.

As an example, the controller 16 receives the malfunction inspectioncommand when it increases the rotation speed of the fan 18 from zero toa normal rotation speed (i.e., when the supply of electric power fromthe inverter 32 to the fan motor 30 is started) in order to normallyoperate the fan 18.

As another example, the controller 16 receives the malfunctioninspection command when it decreases the rotation speed of the fan 18from the normal rotation speed to zero (i.e., when the supply ofelectric power from the inverter 32 to the fan motor 30 is stopped) inorder to stop the fan 18 in normal operation.

As still another example, the controller 16 receives the malfunctioninspection command when the process is interrupted during the normaloperation of the fan 18. Note that, the above-described normal rotationspeed is pre-set as a required value for normally operating the fan 18.

At step S1, the controller 16 changes the rotation speed of the fan 18.As an example, as shown in FIG. 4, the controller 16 sends a rotationspeed changing command to the inverter 32 so as to decrease the rotationspeed R of the fan 18, which is rotating at the rotation speed R₂ (e.g.,the normal rotation speed), from the rotation speed R₂ to the rotationspeed R₁ (e.g., zero).

As another example, as shown in FIG. 5, the controller 16 sends arotation speed changing command to the inverter 32 so as to increase therotation speed R of the fan 18, which is rotating at the rotation speedR₄ (e.g., zero), from the rotation speed R₄ to the rotation speed R₅(e.g., normal rotation speed).

The inverter 32 controls electric power supplied to the fan motor 30 soas to change the rotation speed R of the fan 18 to a rotation speed (R₁or R₅) in accordance with the rotation speed changing command receivedfrom the controller 16. Thus, in this embodiment, the controller 16functions as a fan controller 42 (FIG. 2) which controls the operationof the fan 18.

At step S2, the controller 16 acquires a rotation speed R_(x) of the fan18. Specifically, the controller 16 sends a command to the rotationspeed detecting part 19 so as to detect the rotation speed R_(x) of therotator 28 of the fan 18 at this time. The controller 16 receives dataof the rotation speed R_(x) from the rotation speed detecting part 19,and records it on the storage 24.

As an example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the rotation speed R_(x) measured at step S2substantially coincides with the rotation speed R₂ at the time point t₁in FIG. 4.

As another example, when the rotation speed R is increased from R₄ to R₅at step S1 (FIG. 5), the rotation speed R_(x) measured at step S2substantially coincides with the rotation speed R₄ at the time point t₄in FIG. 5.

At step S3, the controller 16 start to time an elapsed time.Specifically, the controller 16 sends a timing start command forstarting to time an elapsed time to the timer 22. The timer 22 times anelapsed time t from a time point when it receives the timing startcommand from the controller 16.

At step S4, the controller 16 acquires a rotation speed R_(y) of the fan18 when the elapsed time t timed by the timer 22 reaches a predeterminedtime. The predetermined time is pre-stored in the storage 24.

As an example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the predetermined time is set to the above-mentionedtime period t¹⁻². As another example, when the rotation speed R isincreased from R₄ to R₅ at step S1 (FIG. 5), the predetermined time isset to above-mentioned the time period t⁴⁻⁵.

At this step S4, when the predetermined time (e.g., time period t¹⁻² ort⁴⁻⁵) has elapsed from a time point (e.g., time point t₁ in FIG. 4 ortime point t₄ in FIG. 5) when the controller 16 has sent the rotationspeed changing command to the fan 18 at step S1, the controller 16 sendsa command to the rotation speed detecting part 19, similar to step S2,so as to acquire the rotation speed R_(y) of the fan 18 at this time.

At step S5, the controller 16 acquires a relationship between time t androtation speed R (i.e., t−R relationship). As an example, the controller16 calculates, as a parameter representing the t−R relationship, anamount of change δR_(xy)=|R_(x)−R_(y)|(this value corresponds to theabove-mentioned δR) from the rotation speed R_(x), acquired at step S2to the rotation speed R_(y) acquired at step S4.

As another example, the controller 16 calculates a ratioR=δR_(xy)/δR_(ref) as a parameter representing the t−R relationship. Asstill another example, the controller 16 calculates a gradient δR/δt(corresponding to e.g. (R₂−R₁) /t¹⁻² or (R₆−R₄)/t⁴⁻⁵ described above) asa parameter representing the t−R relationship.

Thus, in this embodiment, the controller 16 functions as a relationshipacquiring part 44 (FIG. 2) which acquires a relationship (i.e., t−Rrelationship) between the time t from the time point t₁ (t¹⁻² or t⁴⁻⁵),at which the rotation speed R of the fan 18 is changed, and the rotationspeed R of the fan 18.

At step S6, the controller 16 determines whether the t−R relationshipacquired at step S5 is different from a predetermined standard. As anexample, when the amount of change δR_(xy)=|R_(x)−R_(y) is calculated atstep S5, the controller 16 compares the calculated amount of changeδR_(xy) with a threshold value α_(l) which is set with respect to thestandard δR_(ref).

For example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the controller 16 determines whether the amount ofchange δR_(xy) is greater than the threshold value α₁ (e.g.,α₁=δR_(ref)×1.1) .

On the other hand, when the rotation speed R is increased from R₄ to R₅at step S1 (FIG. 5), the controller 16 determines whether the amount ofchange δR_(xy) is smaller than the threshold value α₁ (e.g.,α₁=δR_(ref)×0.9).

When the amount of change δR_(xy) is greater (or smaller) than thethreshold value α₁, the controller 16 determines that the t−Rrelationship of the fan 18 is different from the standard δR_(ref)(i.e., determines “YES”).

As another example, when the ratio R is calculated at step S5, thecontroller 16 compares the ratio R with a predetermined threshold valueα₂ which is pre-set with respect to the ratio R.

For example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the controller 16 determines whether the calculatedratio R is greater than the threshold value α₂ (e.g., α₂=1.1). On theother hand, when the rotation speed R is increased from R₄ to R₅ at stepS1 (FIG. 5), the controller 16 determines whether the calculated ratio Ris smaller than the threshold value α₂ (e.g., α₂=0.9).

When the ratio R is greater (or smaller) than the threshold value α₂ thecontroller 16 determines that the t−R relationship of the fan 18 isdifferent from the standard δR_(ref) (i.e., determines “YES”).

As still another example, when the gradient δR/δt is calculated at stepS5, the controller 16 compares the absolute value of the gradient|δR/δt|, with a threshold value α₃ which is set with respect to thestandard δR_(ref)/δt .

For example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the controller 16 determines whether the absolutevalue of gradient |δR/δt| is greater than the threshold value α₃ (e.g.,α₃=|δR_(ref)/δt|×1.1).

On the other hand, when the rotation speed R is increased from R₄ to R₅at step S1 (FIG. 5), the controller 16 determines whether the absolutevalue of gradient |δR/δt| is smaller than the threshold value α₃ (e.g.,α₃=|δR_(ref)/δt|×0.9).

When the absolute value of gradient |δR/δt| is greater (or smaller) thanthe threshold value α₃, the controller 16 determines that the t−Rrelationship (δR/δt) of the fan 18 is different from the standardδR_(ref)/δt (i.e., determines “YES”). Note that, the above-mentionedthreshold value α₁, α₂, or α₃ is pre-stored in the storage 24.

When the controller 16 determines “YES” at this step S6, the controller16 proceeds to step S7. On the other hand, when the controller 16determines that the t−R relationship is not different from the standard(i.e., determines “NO”), the controller 16 ends the flow shown in FIG.6.

Thus, in this embodiment, the controller 16 functions as a malfunctiondetermining part 46 (FIG. 2) which determines whether the t−Rrelationship of the fan 18 is different from the standard.

At step S7, the controller 16 generates a malfunction notifying signalindicating that a malfunction occurs in the fan 18. As an example, thecontroller 16 generates the malfunction notifying signal in the form ofa sound signal of an alarm to be output to a user.

As another example, the controller 16 generates the malfunctionnotifying signal in the form of an image signal of an alarm visible to auser. Thus, in this embodiment, the controller 16 functions as amalfunction signal generating part 48 (FIG. 2) which generates themalfunction notifying signal.

At step S8, the controller 16 notifies a user of the occurrence of amalfunction in the fan 18 via the alarm output part 20. As an example,when the sound signal of an alarm is generated at step S7, thecontroller 16 sends the sound signal to the alarm output part 20. Inthis case, the alarm output part 20 includes a speaker to output thereceived sound signal as an alarm sound.

As another example, when the image signal of an alarm is generated atstep S7, the controller 16 sends the image signal to the alarm outputpart 20. In this case, the alarm output part 20 includes a display partto display the alarm image corresponding to the received image signal.

In this way, the user can recognize the occurrence of a malfunction inthe fan 18 from the alarm sound or the alarm image. Consequently, theuser can recognize that it is necessary to carry out maintenance forremoving foreign substances attached to the rotator 28 of the fan 18.

As described above, in this embodiment, the relationship betweenrotation speed R and time t when the rotation speed R of the fan 18 ischanged (i.e., the amount of change in the rotation speed R over time)is compared with the relationship of the normal product as a standard,so as to determine whether the rotation speed R of the fan 18 is equalto that of the normal product.

According to this configuration, a malfunction in the rotation speed Rof the fan 18 can be more accurately detected, and therefore it ispossible to reliably avoid erroneously detecting a malfunction in thefan 18, and thereby avoid unnecessarily stopping the operation of themotor drive device 10. As a result, it is possible to improve theefficiency of operation.

Next, with reference to FIG. 7, another example of the operation flow ofthe motor drive device 10 will be described. Note that, in the operationflow shown in FIG. 7, steps similar to those in FIG. 6 are assigned thesame numeral references, and the detailed description thereof will beomitted.

After step S1, at step S11, the controller 16 starts to measure therotation speed R of the fan 18. Specifically, the controller 16 sends acommand to the rotation speed detecting part 19 so as to periodicallydetect the rotation speed R of the rotator 28 of the fan 18 at a periodτ(e.g., 0.5 sec.). The controller 16 receives data of the rotation speedR from the rotation speed detecting part 19 at the period τ, and storesthem in the storage 24.

At step S12, the controller 16 determines whether the rotation speed Rof the fan 18 detected at step S11 reaches a predetermined target valueR_(t).

As an example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the target value R_(t) is set to the rotation speedR₁. As another example, when the rotation speed R is increased from R₄to R₅ at step S1 (FIG. 5), the target value R_(t) is set to the rotationspeed R₅.

When the controller 16 determines that the rotation speed R detected atstep Sll reaches the target value R_(t) (i.e., determined “YES”), itproceeds to step S13. On the other hand, when the controller 16determines that the rotation speed R does not reach the target valueR_(t) (i.e., determines “NO”), it repeats step S12.

At step S13, the controller 16 functions as the relationship acquiringpart 44 (FIG. 2) so as to acquire the relationship between time t androtation speed R (i.e., the t−R relationship). Specifically, thecontroller 16 acquires, as a parameter representing the t−Rrelationship, the elapsed time t timed by the timer 22 at the time pointwhen it is determined “YES” at step S12, and stores it in the storage24.

For example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the elapsed time t timed at this time pointcorresponds to the time period (t¹⁻²) from the time point (t₁) when thecontroller 16 sends the rotation speed changing command at step S1 tothe time point (t₂) when the rotation speed R reaches R₁.

On the other hand, when the rotation speed R is increased from R₄ to R₅at step S1 (FIG. 5), the elapsed time t timed at this time pointcorresponds to the time period (t⁴⁻⁶) from the time point (t₄) when thecontroller 16 sends the rotation speed changing command at step S1 tothe time point (t₆) when the rotation speed R reaches R₅.

At step S14, the controller 16 functions as the malfunction determiningpart 46 (FIG. 2) so as to determine whether the t−R relationshipacquired at step S13 is different from a predetermined standard.

As an example, when the rotation speed R is decreased from R₂ to R₁ atstep S1 (FIG. 4), the controller 16 determines whether the elapsed timet (time period t¹⁻²) acquired at step S13 is smaller than a thresholdvalue α₄ (e.g., α₄=t¹⁻³×0.9) set for the above-described standard (timeperiod t¹⁻³).

As another example, when the rotation speed R is increased from R₄ to R₅at step S1 (FIG. 5), the controller 16 determines whether the elapsedtime t (time period t⁴⁻⁶) acquired at step S13 is greater than thethreshold value α₄ (e.g., α₄=t⁴⁻⁵×1.1) set for the above-describedstandard (time period t⁴⁻⁵). The threshold value α₄ is pre-stored in thestorage 24. When the elapsed time t is greater (or smaller) than thethreshold value α₄, the controller 16 determines that the t−Rrelationship of the fan 18 is different from the standard (time periodt¹⁻³ or time period t⁴⁻⁵) (i.e., determines “YES”).

The controller 16 proceeds to step S7 when it determines “YES”. On theother hand, the controller 16 ends the flow shown in FIG. 7 when itdetermines that the t−R relationship is not different from the standard(i.e., determines “NO”).

Thus, according to the operation flow in FIG. 7, a malfunction in therotation speed R of the fan 18 can be accurately detected, similar tothe flow in FIG. 6. Therefore, it is possible to avoid erroneouslydetecting a malfunction in the fan 18, and thereby avoid unnecessarilystopping the operation of the motor drive device 10. As a result, it ispossible to improve the efficiency of operation.

Note that, at least one of the timer 22 and the storage 24 may beincorporated in the controller 16, or in an external device (e.g.,server) communicably connected to the controller 16 via a network.

Although the invention has been described above through variousembodiments, the embodiments do not limit the inventions according tothe claims. Further, a configuration obtained by combining the featuresdescribed in the embodiments of the invention can be included in thetechnical scope of the invention. However, all combinations of thesefeatures are not necessarily essential for solving means of theinvention. Furthermore, it is obvious for a person skilled in the artthat various modifications or improvements can be applied to theembodiments.

Regarding the order of operations, such as actions, sequences, steps,processes, and stages, in the devices, systems, programs, and methodsindicated in the claims, specification and drawings, it should be notedthat the terms “before”, “prior to”, etc. are not explicitly described,and any order can be realized unless the output of a previous operationis used in the subsequent operation. Regarding the processing in theclaims, specification, and drawings, even when the order of operationsis described using the. terms “first”, “next”, “subsequently”, “then”,etc., for convenience, maintaining this order is not necessarilyessential for working the inventions.

1. A motor drive device comprising: a fan; a fan controller whichcontrols the fan; a rotation speed detecting part which detects arotation speed of the fan; a relationship acquiring part which acquiresa relationship between a time elapsed from a time point, at which thefan controller changes the rotation speed, and the rotation speeddetected by the rotation speed detecting part; a malfunction determiningpart which determines whether the relationship acquired by therelationship acquiring part is different from a predetermined standard;and a malfunction signal generating part which generates a signalindicating that a malfunction occurs in the fan when the malfunctiondetermining part determines that the relationship is different from thestandard.
 2. The motor drive device according to claim 1, wherein therelationship acquiring part acquires, as the relationship, an amount ofchange in the rotation speed detected by the rotation speed detectingpart within a time period until a predetermined time elapses from thetime point at which the fan controller sends to the fan a command forchanging the rotation speed, wherein the malfunction determining partdetermines that the relationship is different from the standard when theacquired amount of change is greater or smaller than a predeterminedthreshold value.
 3. The motor drive device according to claim 1, whereinthe relationship acquiring part acquires, as the relationship, a ratioof an amount of change in the rotation speed detected by the rotationspeed detecting part within a time period until a predetermined timeelapses from the time point at which the fan controller sends to the fana command for changing the rotation speed, to the standard, wherein themalfunction determining part determines that the relationship isdifferent from the standard when the ratio is greater or smaller than apredetermined threshold value.
 4. The motor drive device according toclaim 1, wherein the relationship acquiring part acquires, as therelationship, a time until the rotation speed detected by the rotationspeed detecting part changes from a first rotation speed to a secondrotation speed different from the first rotation speed when the fancontroller sends to the fan a command for changing the rotation speedfrom the first rotation speed to the second rotation speed, wherein themalfunction determining part determines that the relationship isdifferent from the standard when the acquired time is greater or smallerthan a predetermined threshold value.
 5. The motor drive deviceaccording to claim 1, further comprising a timer which measures the timefrom the time point at which the fan controller changes the rotationspeed.
 6. The motor drive device according to claim 1, furthercomprising a storage which stores the rotation speed detected by therotation speed detecting part or the time from the time point at whichthe fan controller changes the rotation speed.
 7. The motor drive deviceaccording to claim 1, further comprising an alarm output part whichreceives the signal and outputs an alarm to a user.
 8. A method ofnotifying a user of an occurrence of a malfunction in a fan provided ata motor drive device, comprising: changing a rotation speed of the fan;detecting the rotation speed when changing the rotation speed; acquiringa relationship between a time elapsed from a time point, at which therotation speed is changed, and the detected rotation speed; determiningwhether the acquired relationship is different from a predeterminedstandard; and notifying to a user that a malfunction occurs in the fanwhen determining that the relationship is different from the standard.